Unit 2 Test Review - Genetics Flashcards
What does DNA stand for? What does it contain
-deoxyribonucleic acid
-contains the genetic information of a cell
What does DNA look like?
-double helix (ladder twisted in a clockwise direction)
What is DNA composed of? What are the four chemicals in DNA?
-deoxyribose sugars and phosphates groups (sides) and a nitrogenous base
-the four chemicals in DNA are adenine, thymine, cytosine, and guanine
What is the most basic unit of a DNA molecule? What is it made up of?
-a nucleotide
-a sugar, a phosphate group, and one of four nitrogenous bases
What is the definition of a gene? What do genes make?
-a portion/tiny section of DNA, which contains specific information which codes for particular proteins/traits
-genes make up chromosomes
-basic unit of heredity
What is chromatin?
-fibres of DNA in its uncondensed form (found in the nucleus in this specific form)
What is a chromosome?
-a structure in the nucleus that contains DNA on which a gene occupies a specific location
What two kinds of cells are multicellular organisms made out of?
-Somatic (body) cells
-Reproductive (sex cells)
What are Somatic cells?
-two sets, or the diploid (2n) number of chromosomes
-all organisms have a certain amount of chromosomes in their body cells
(human somatic cells have 46 chromosomes meaning 23 pairs called homologous chromosomes)
What are homologous chromosomes?
-similar in size and shape, and they code for the same trait. Each parent contributes one chromosome to a homologous pair.
What are sex cells(gametes)?
-contain a single set (haploid number n) of chromosomes
-gametes do not have homologous chromosomes, instead, they have one chromosome from each pair
-in the case of human gametes, we have 23 pairs of chromosomes altogether including the gametes
What are the three parts of the cell cycle, and what do they do?
1) interphase
2) mitosis (nuclear division)
3) cytokinesis (cell division)
What is interphase? (1)
-most of the cell life cycle is spent here
-there are three phases:
1) G1, cell growth and differentiation
2) S, synthesis and each chromosome is duplicated
3) G2, cell growth
What is mitosis? (2)
-nuclear division, divides the nucleus
-mother cell divides into two identical daughter cells
-mitosis ensures genetic continuity as the same genetic information is stored in the nucleus
What is cytokinesis? (3)
-cell division, a cell divides the cytoplasm into two new daughter cells
What is meiosis?
-cell division that produces gametes with the number of chromosomes from the original cell reduced by half through separation of homologous chromosomes (occurs in sex organs only)
When does meiosis begin to occur in humans?
males (xy): begins at puberty (age 9-19)
females (xx): all eggs are produced before birth and at puberty the eggs mature
Why is meiosis important?
-consists of two specialized cells known as gametes forming a zygote
-since meiosis reduces the chromosomal content by half and thus the union of the sex cells restores the diploid number and maintains the viability of the organism (if this didn’t happen, the zygote would have twice as much genetic information as needed)
What is a zygote cell?
-fertilized egg
What is fertilization?
-egg and sperm uniting
What is an embryo?
-organism in early stages of development
What are unique events in meiosis?
-homologous chromosomes pair up before division
-these homologous chromosomes look alike, code for the same traits, and one is from each parent
What is crossing over, and what’s its significance?
-occurring during prophase I, the homologous chromosomes pair up in tetrads in a process called synapsis and have certain overlapping sections that break off and switch and exchange genetic material
-they separate in the 2nd division of meiosis completely, and this is significant as it indicates genetic variation in the gametes, this is a reason why siblings look different from one another
What are alleles?
-alternate forms of genes controlling a given characteristic, found at the loci’s on homologous chromosomes
What is a Punnett square?
-a chart used to show the possible gene combinations of alleles between the two gametes of two individuals
What is a genotype?
-the actual gene makeup of an individual
What is a phenotype?
-the specific physical characteristic, dependent on the genotype and its interaction with the environment
What does homozygous mean?
-the alleles for a characteristic code are the same (two dom alleles, or two recessive)
What does heterozygous mean?
-the alleles for a characteristic code for a different trait (gene pair with dominant allele or recessive allele)
What is dominant vs recessive?
-the dominant is the allele expressed in the present heterozygous form
-the recessive is the trait expressed in the homozygous form and the one masked in the heterozygous form
What is the normal chromosomal count in humans?
-22 pairs of autosomal chromosomes (homologous)
-1 pair of sex cells (gametes)
What is Non-disjunction?
-the failure of a pair of chromosomes to properly separate during meiosis
-results in one gamete having too many chromosomes and the other having too few
In Non-disjunction what is monosomy vs trisomy?
monosomy:
-loss of one autosome
-does not support life
-zygote gets 1 copy of chromosome
trisomy:
-gain of one autosome
-trisomy gets 3 copies of chromosome instead of 2
-does not support life in most cases
(supports 12,13,15,18,21 for a time)
Trisomy 13
-patau syndrome
-1 in 25000 births
-impaired growth
slowed mental development
-malformed ears
-absence of eyes (sometimes)
-cleft lip and palate
-polydactyly
-characteristic hand clench
-rocker-bottom charcot feet
Trisomy 18
-edward’s syndrome
-1 in 8000 births
-severe developmental disabilities
-failure to thrive and often severe malformation of the heart
-receding jaw
-low set ears
-characteristic hand clench
-rocker-bottom charcot feet
Trisomy 21
-down syndrome
-1 in 750 births
-delayed maturation of the skeletal system resulting in short stature with poor muscle tone
-this affects mental development, mild to moderate intellectual disabilities
-characteristic facial features such as fold of eye, small and round head, protruding tongue
What are the causes of Non-disjunction in sex chromosomes?
-radiation
-viruses (measles)
-drugs (LSD)
-age of parent
XXX
-1 out of 1000 females
-sterile, but usually normal otherwise
X
-turner’s syndrome
-1 out of 2000 females
-sterile, short-webbed neck, underdeveloped sex organs, low metal development
XXY
-klinfelter syndrome
-1 out of 500 males
-sterile, tall, and thin, relatively long legs and female body characteristics
Y
-not viable
-the genes on the X chromosome are required
XYY
-1 out of 1000 males
-normal males, may exhibit aggressive behaviour, tall
What are congenital disabilities?
-different from genetic disorders
-not inherited
-occur during fetal development
both gene disorders and congenital liabilities (not always) can be detected before a baby is born
What is genetic counselling?
-genetic counselling can help parents determine the likelihood of their child being born with a genetic disorder
-they study the family histories of both parents and create pedigree charts to trace the passage of traits
What do medical geneticists do?
-analyze blood tests and determine if parents are carriers of certain gene disorders
Can genetic counselling determine if a child will be born with a genetic disorder?
-no, they just determine the likelihood of the child being born with the disorder
What are the two main ways to diagnose genetic disorders?
Analysis of fetal cells:
-amniocentesis
-chorionic villus biopsy
Imaging Techniques:
-ultrasonography
-fetoscopy
What is amniocentesis? (diagnosing genetic disorders)
amniotic fluid: fluid that surrounds a fetus inside the uterus (also contains fetal cells)
-a sample of amniotic fluid is taken and cells are grown in a lab
-can be used to make karyotype (10 days to grow enough cells
-detects chromosome abnormalities
-cannot be conducted until the 14th week of pregnancy
What is spermatogenesis?
-the production of mature sperm cells
What is oogenesis?
-the production of mature egg cells
What is gametogenesis?
-the production of gametes (sex cells) in animals
What is Chronic Villus Biopsy?(diagnosing genetic disorders)
-chronic villi are structures that help maximize the surface area and gas exchange between a mother and a developing fetus (part of the placenta)
-the villi develop from fetal cells and therefore have the same chromosomes as the fetus and amniotic fluid
-a sample of these cells can then be taken and analyzed as in amniocentesis
-can be done as early as the 9th week of pregnancy
What is Ultrasonography? (diagnosing genetic disorders)
-an ultrasound uses high-frequency soundwaves which bounce off of tissue
-depending on the density of the tissue, waves “echo” back at different wavelengths and are used to produce a computerized image called an echogram
-this is used in most pregnancies to detect the position and anatomy of the fetus
-used within amniocentesis to reduce the risk of injury
-can also help doctors detect abnormalities such as congenital health defects
What is fetoscopy? (diagnosing genetic disorders)
-a small incision is made in a pregnant woman’s abdomen
-an endoscope tube is inserted through that incision
-it has a camera on the end that shows an image on a monitor
-instruments can be inserted through the endoscope to perform additional procedures
What is the developing cure for genetic disorders?
gene therapy
-introducing normal genes into the cells of people with defective alleles
-using viruses to inject alleles into cells
-enclosing alleles into droplets of fat, which are taken into cells by endocytosis
(currently, these are all experimental procedures and have limited success)
Who was Gregor Mendel? When was he born?
-Austrian monk who became known as the father of genetics
-he attempted to explain the inheritance of traits from generation to generation
-1822-1884
-important because his results were qualifiable
What were the seven characteristics of pea plants studied by Mendel?
seed shape, colour
flower colour
pod shape, colour
flower position
stem height
Pollination
-the act of transferring pollen grains from the male anther of a flower to the female stigma
Explain the notation used in monohybrid crosses
P1: original parent generation
F1: first filial generation
F2: second filial generation
What is a test cross used for?
-to determine if an allele from the parental generation is homozygous dominant or heterozygous dominant
What is a dihybrid cross?
-a cross of two individuals that differ in two traits of two different genes, follows the inheritance of two traits form parents to offspring
What is the principle of dominance?
-when the two alleles of a pair are different, one is fully expressed and the other is completely masked. The one expressed is called the dominant allele/trait and the one masked is recessive.
What is Mendel’s first law?
-the law of segregation
allele pairs segregate during gamete formation, and the paired condition is restored by random fuison of gametes at fertilization
What is Mendel’s second law?
-the law of independent assortment
when parents differ in two or more characteristics the occurrence of one characteristic in the next generation will be independent of the occurrence of any other characteristic. Characteristics are inherited independently of one another
(this is true if the genes are located on different chromosomes)
What is incomplete dominance? (non-mendelian genetics)
-occurs when one of the alleles does not completely mask the other
-neither is dominant recessive
-its a blending of the two traits
-the heterozygous genotype formed gives a third phenotype called an intermediate
What is co-dominance? (non-mendelian genetics)
-both alleles for a trait are dominant
-its based on interpretation, the third trait confirms co-dominance as its the first two combined as a whole trait
What is multiple alleles? (non-mendelian genetics)
-genes that have more than two alleles
What are the four possible blood types in humans as a result of the glycoproteins in the human body?
Type A: I^A I^A or I^Ai
Type B: I^B I^B or I^Bi
Type AB: I^A I^B
Type O: ii
What is sex linkage?
-the pattern of inheritance resulting from genes located on the X chromosome
-most of the genes located on the x chromosome are unrelated to sex determination
Do some genetic disorders result from a recessive allele carried on the X chromosome?
-yes
Who identified the inheritance pattern of sex linkage?
-thomas morgan, through the study of fruit flies
What is the process of transferring recessive traits in sex linkage?
-if the x chromosome that a male receives from his mom carries a recessive allele, he will express the disorder since the Y chromosome does not carry another allele to mask it
-a female on the other hand will only express the condition if she is homozygous recessive (her father had to have had the gene and her mother had to be a carrier)
so, more males than females tend to have disorders that are related to sex-linked recessive traits
What are pedigrees?
-diagram of individual ancestors that is used in human genetics to analyze the inheritance of a certain trait
-used in the breeding of plants and animals as well
Three traits differing punnett squares and pedigrees
Punnett Squares
-probabilities of certain genotypes/phenotypes associated with offspring
-hypothetical (probability)
-future (unborn)
Pedigrees
-tracking of the inheritance of a trait throughout the history of a family
-real history
-past (alive or once alive)
Define the following:
Critical Mating
dominant
recessive
critical mating:
two parents with the same phenotype and, child with a different
dominant:
affected parents, unaffected child
recessive:
unaffected parents affected child
What is autosomal inheritance?
-autosomal dominant disorder occurs when a disease-causing allele is dominant and an individual has one or both copies of the allele (AA or Aa)
-autosomal recessive is when the disease-causing allele is recessive and an individual has both copies (aa), (Aa is a carrier)
Where is mitosis happening?
-in body tissues to replace lost cells
-during growth
-at the site of an injury
-formation of tumours
-when single-celled organisms reproduce
Why do cells divide (mitosis)?
different types of cells spend different times in the phases of the cell cycle
-maximum growth theory: surface-to-volume ratio becomes insufficient to support efficiency in the cell’s functions
-contact inhibition: neighbouring cells tell the cell to divide using protein messages
What are human karyotypes?
-a photograph of the chromosomes od a cell ar a time when the chromosome cosists of two sister chromatids attached to each other at the centromere
-occurs during metaphase in mitosis (they are called mitotic metaphase chromosomes)
-pair 1- 22 are autosomal chromosomes
-pair 23 are the gametes (sex cells)
